Solve small string and API tasks

You are given three small programming tasks (typical “easy” difficulty). Implement each as a function.

Task 1: Validate parentheses

Given a string s consisting only of the characters '(' , ')' , '{' , '}' , '[' , ']', determine whether it is valid.

A string is valid if:

• Open brackets are closed by the same type of brackets.
• Open brackets are closed in the correct order.
• Every close bracket has a corresponding open bracket.

Input: s (length 0…1e5)

Output: true if valid, else false

Task 2: Longest substring without repeating characters

Given a string s (ASCII), return the length of the longest substring that contains no repeated characters.

Input: s (length 0…2e5)

Output: integer length

Task 3: Fetch from a public GET API and transform

You are given a public HTTP GET endpoint that returns JSON.

Assume the endpoint returns an array of records in the form:

[
  {"id":"a1","group":"books","amount":12,"ts":"2026-01-01T10:00:00Z"},
  {"id":"a2","group":"books","amount":7,"ts":"2026-01-01T11:00:00Z"},
  {"id":"b1","group":"games","amount":20,"ts":"2026-01-02T09:00:00Z"}
]

Write code that:

1. Calls the endpoint.
2. Parses the JSON.
3. Produces a summary per group with:
   • count of records
   • totalAmount (sum of amount )
4. Returns the summary list sorted by group ascending.

Constraints/notes:

• Records may be empty.
• amount is a non-negative integer.
• You may assume the response fits in memory (≤ 1e5 records).
• Focus on correctness and clean error handling (HTTP errors, invalid JSON).